While wire strippers of various types have become common heretofore, a part of the wire coating is cut and stripped away by use of a cutter in most cases.
When stripping the coating, it is necessary to feed the blade into the wire coating as deeply as possible in order to cut the wire coating more precisely and sharply. The wire core may, however, be subject to be scratched or a part of it may be cut off if the blade comes in contact with the wire core to result in rejection of the electric wire concerned.
Since absolute safety is demanded especially for the electric wire for automotive or aircraft industries, even an electric wire having the slightest scratches on its core is rejected for the reason that it may be damaged and lead to serious accidents if used for movable parts or in any position subject to vibrations because of stress concentration on the scratches.
A function to detect any contact between the wire core and the stripping blade is, therefore, deemed as indispensable for the wire stripper so that a number of automatic wire strippers developed in recent years are provided with the said function of contact detection. Most of them, however, use a method to detect any contact between the wire core and the blade through detection of electric conduction between electrodes which are allocated to them, respectively.
As an example, a wire stripper according to the patent document (Japanese Patent Opening No. 87643/1995) referred to later is described in the following while taking FIG. 9 as the basis.
According to this heretofore known technique, an electric wire 63 is led through a wire guide 84 and fastened by a wire gripper 85. A cassette blade 86 is then put into operation to make an incision on an insulating coating 71 of a core 70 of the electric wire 63 by means of incision making cutters 87 and to cut the electric wire 63 by means of cutting blades 82 so as to strip the coating by simultaneously pulling it axially by means of a wire gripper 85.
When the incision making cutters 87 in the cassette blade 86 come now in contact with the wire core 70 in the phase of incision to the coating 71, an alternating current flows through it by way of a capacitance arising between the electric wire 63 and the wire gripper 85, a detector 88 and an AC power supply 89 in the said order. A voltage corresponding to this current is detected by the detector 88 to confirm the contact of the incision making cutter 87 with the wire core 70.